Here's my settings. I'm currently testing out all of my settings. Trying to fine tune it still. Since GT4 has so many cars that I love I just quickly tune one to another, drive it, tune it, then move onto a new car. Then go back and slowly properly tuning it.
Here's a track setting for my Spec C.
Springs - 13/12
rebound/inbound -
8/8
10/10
rideheight - 5 clicks to right from lowest/same
camber - -2.2/-2.0
toe - -1/-2
stabilizer - 6/7
FC LSD
20/30
30/45-50; I'm currently running on 50
5/20
VCD - Set power to rear(10%)
TCS - Off
downforce - 30/30(MAX); I gave it a GT wing since it doesn't come with a wing.
Racing supersoft tires.